1. Field of Invention
This invention relates to an electrode assembly, and production method, incorporated in image recording apparatuses, such as copy machines, printers, plotters, and facsimile machines, for use in the recording processes.
2. Description of Related Art
In general, an electrode assembly used in a recording process comprises a plurality of apertures, and the same number of control electrodes positioned so as to face the associated apertures. This type of electrode is called an aperture electrode. It is typically used in toner jet image recording apparatuses, in which toner particles travel in an electric field toward a recording medium to form an image on the recording medium. An example of an image recording apparatus using an aperture electrode is disclosed in Japanese Patent Application Laid-open No. 6-155798. In this publication, a predetermined voltage, based on the image data, is applied to each of the control electrodes to control the passage of toner particles (i.e., the charged particles) through the corresponding aperture. The toner particles that pass through the apertures form an image on a recording medium based on the image data.
The electrode assembly comprises an insulating film made of, for example, polyimide; control electrodes formed on the top surface of the insulating film; a top coating layer covering both the control electrodes and the insulating film; and apertures formed with the control electrodes therearound penetrating through the top coating layer and the insulating film. The top coating layer is provided for the purpose of protecting the control electrodes which are formed along the minute interconnection pattern on the insulating film. This coating layer is an insulator formed from, for example, Yupicoat (Trademark), which is a polyimide coating material manufactured by UBE Industries, Ltd., by a screen printing method through the printing, drying, and baking steps.
However, because the top coating layer is an insulating layer, this layer becomes charged during the operation of the conventional image recording apparatus having recording electrodes, which adversely affects the toner particles that pass through the apertures and fly to the recording medium.
For example, if the polyimide of the top coating layer is negatively charged, an electrostatic field repulsing the negatively charged toner particles is formed over the entire surface of the aperture electrode assembly. The leakage electric field is also formed in the apertures, which prevents the toner particles from passing through the apertures.
If the polyimide is positively charged, an electrostatic field that attracts the negatively charged toner particles is formed over the entire surface of the aperture electrode assembly, and its leakage field is formed in the apertures. This causes the negatively charged toner particles to attach to and accumulate in the apertures, which results in choked apertures.